Add Python unit testing and coverage report to "make check"

Add Python unit testing and coverage report to "make check"

If --enable-python is included in the arguments to configure, "make check"
runs all Python unit tests using nosetests and generates a testing coverage
report for all Python code.

The original json_test.py is factored out to provide a separate file for
testing osrf.net_obj vs. osrf.json vs. osrf.*, when we eventually get there.

Signed-off-by: Dan Scott <dan@coffeecode.net>
git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@2244 9efc2488-bf62-4759-914b-345cdb29e865